Light pollution reduces activity, food consumption and growth rates in a sandy beach invertebrate

Highlights

• Effects of ecological light pollution (ELP) were experimentally tested.

• A widespread sandy beach amphipod was used as a model species.

• ELP reduced amphipod's locomotor activity, food consumption and growth rate.

Abstract

The continued growth of human activity and infrastructure has translated into a widespread increase in light pollution. Natural daylight and moonlight cycles play a fundamental role for many organisms and ecological processes, so an increase in light pollution may have profound effects on communities and ecosystem services. Studies assessing ecological light pollution (ELP) effects on sandy beach organisms have lagged behind the study of other sources of disturbance. Hence, we assessed the influence of this stressor on locomotor activity, foraging behavior, absorption efficiency and growth rate of adults of the talitrid amphipod Orchestoidea tuberculata. In the field, an artificial light system was assembled to assess the local influence of artificial light conditions on the amphipod's locomotor activity and use of food patches in comparison to natural (ambient) conditions. Meanwhile in the laboratory, two experimental chambers were set to assess amphipod locomotor activity, consumption rates, absorption efficiency and growth under artificial light in comparison to natural light-dark cycles. Our results indicate that artificial light have significantly adverse effects on the activity patterns and foraging behavior of the amphipods, resulting on reduced consumption and growth rates. Given the steady increase in artificial light pollution here and elsewhere, sandy beach communities could be negatively affected, with unexpected consequences for the whole ecosystem.

Introduction

Natural light sources (sunlight and moonlight) play a fundamental role on an array of organisms and ecological processes (Gaston et al., 2012). For example, the light of stars provides essential signals for long distance migration of birds (Åkesson et al., 2001) as well as direction to nocturnal insects (Verheijen, 1985). Sunlight and moonlight are also key drivers of circadian rhythms (Scapini et al., 1997), nocturnal migrations of pelagic organisms (Ringelberg, 1999) and modulators of predator-prey interactions (e.g., Clarke, 1983, Kotler et al., 1991), among many other processes. In this context, human alteration of natural light cycles is likely to lead to important effects on biological processes and diversity. A 6% annual increase in worldwide artificial lighting due to the rise of human infrastructure and activity (Hölker et al., 2010), has triggered concerns about the potential impact of this stressor on a variety of organisms and communities (Longcore and Rich, 2004, Hölker et al., 2010, Gaston et al., 2012).

Ecological light pollution (hereafter ELP) is the “artificial light that alters the natural patterns of light and dark in ecosystems” (Longcore and Rich, 2004). Among the best understood effects of ELP are those documented for sea turtle orientation (Peters and Verhoeven, 1994), facilitated detection of prey by predators (Eisenbeis and Hassel, 2000, Kolligs, 2000, Rydell, 1992, Frank, 2006), visual interference (Le Corre et al., 2002), and alteration of feeding behaviors (Bird et al., 2004). As of 2010, over 20% of the world coastlines (excluding Antarctica) were exposed to some level of artificial lightning (Davies et al., 2014). In these systems, sandy beaches represent over 80% of the ice-free coastline (Short, 1999, Bascom, 1980), and yet, the potential effects of ELP on these habitats remain virtually unknown (Schlacher et al., 2016). Sea turtles are, again, an exception (Witherington and Martin, 2000): we know for example that artificial light networks inhibit turtle nesting in sandy beaches and disorient their hatchlings (Peters and Verhoeven, 1994).

Crustacean amphipods of the family Talitridae are, in terms of biomass and abundance, among the dominant organisms in the upper levels of temperate sandy beaches (e.g., Dahl, 1952, Scapini et al., 1997, Jaramillo et al., 2002). These amphipods play an important community role and accelerate the decomposition of stranded macroalgae wracks (Lastra et al., 2008, Olabarria et al., 2009, Duarte et al., 2010, MacMillan and Quijon, 2012). Most amphipods display distinctive circadian rythms entailing the active search for food during the night hours and the burying in the upper and mid intertidal sediments during daylight (Jaramillo et al., 2003, Dugan et al., 2004, Duarte et al., 2009, Duarte et al., 2014). Among other cues, Talitrid amphipods rely on visual stimuli like the sun and the moon for their orientation and circadian rythms (Mezzetti et al., 2010, Scapini, 2006, Nardi et al., 2000, Scapini et al., 1997). Hence, it is reasonable to think that the widespread growth of artificial lightning would likely alter their activity patterns as well as their feeding behavior.

The Talitrid amphipod Orchestoidea tuberculata is among the numerically dominant species in the upper intertidal zone of exposed sandy beaches of central and southern Chile in the southeastern Pacific (Varela, 1983, Jaramillo et al., 2000, Jaramillo et al., 2003). Activity patterns in this species change along the life cycle: while juveniles are active along the 24 h cycle (Jaramillo et al., 1980), subadults are more active at dusk and night, and adults are strictly nocturnal. Hence, based on their abundance and well known activity patterns, adult O. tuberculata represent ideal models for the study of the ELP in the central Chile coastline. Surprisingly though, little has been done about it with the exception of a survey conducted by Giaconni (2006). This author found abundant populations of this species in all but one sandy beach system which, coincidentally, was the only one exposed to ELP. However, no experimental studies to date have tested the relationship between ELP and any relevant aspects of the ecology of this species. Our study aims to fulfill that knowledge gap by experimentally assessing the influence of ELP on the locomotor activity and feeding ecology of adult O. tuberculata.